Electric motors can be used in many fields of technology. For example, electric motors can be used for pumping liquids. In this case, the electric motors can be operated in a liquid or a liquid can flow through said electric motors.
By way of example, an electric motor can be mechanically commutated with the aid of brushes and a commutator. A corresponding electric motor is known, for example, from DE 10 2006 047 085 A1.
When the electric motor is used to pump fuel, there may be an undesired increase in the electrical resistance between the commuter and the brushes. In particular, there may be an increase in the electrical resistance when the electric motor is used with ethanol-containing fuels and/or during operation at a rated load of the electric motor which is lower than average. This increase in the electrical resistance is called the “filming effect”.